There will be described a background art of the present invention by taking an excavator illustrated in FIG. 6 as an example. This excavator comprises a crawler-type lower propelling body 1, and an upper slewing body 3 mounted on the lower propelling body 1 slewably about a vertical axis. A slewing bearing 2 is interposed between the lower propelling body 1 and the upper slewing body 3, having an inner race fixed on the side of the lower propelling body 1 and an outer race fixed on the side of the upper slewing body 3.
The upper slewing body 3 comprises an upper frame 8 serving as a base, and a work attachment 7 attached to the upper frame 8. The work attachment 7 includes a boom 4 derrickably supported on the upper frame 8, an arm 5 hinged to a distal end of the boom 4, and a bucket 6 attached to a distal end of the arm 5. The upper frame 8 includes a cabin 9 provided in a left front region thereof, an engine room 10 provided in a rear region thereof and having an upward-facing opening, and an engine cover 12 provided to selectively open and close the upper opening of the engine room 10. The engine room 10 houses an engine 11 and various other equipment (these may be collectively called as “engine room equipment” below).
This excavator further comprises a slewing device for slewing the upper slewing body 3. This slewing device comprises: a slewing power source having a slewing power source output shaft; a speed reducer coupled to the slewing power source output shaft and having a speed reducer output shaft, the speed-reducer output shaft adapted to be rotated at a low speed than that of the slewing power source output shaft; a slewing pinion attached to the speed-reducer output shaft; and an internal gear fixed to the inner race of the slewing bearing 2 and meshed with the slewing pinion, the slewing pinion and the internal gear making a mesh movement to thereby transmit a rotational power output of the speed-reducer output shaft to the upper slewing body 3 as a slewing power.
As the slewing power source, a hydraulic motor is used in a hydraulic excavator, and an electric motor (slewing electric motor) is used in a hybrid excavator or an electric excavator. The latter is disclosed, for example, in the following Patent Document 1.
For conventional construction machines including the above excavator, it is an important issue to secure a platform for maintenance work of equipment housed in the engine room 10. In the excavator illustrated in FIG. 6, a maintenance operator opens the engine cover 12 provided on the engine room 10, as illustrated in FIG. 6, and performs maintenance work forward of the engine room 10; in this case, it is difficult to provide a platform for the work within a limited space. Typically used as the platform is equipment (e.g., a hydraulic oil tank or a fuel tank) installed around the engine room 10; however, the platform by utilization of such equipment has such a markedly uneven topography that it is difficult for the operator to perform the work while stably standing thereon.